1. Field of the Invention
The present invention relates to an ink jet recording apparatus using an ink jet head provided with ink discharge ports to record on a recording medium arranged for a recording area. More particularly, the invention relates to an ink jet recording apparatus capable of significantly reducing adverse effects to be produced on the quality of recorded images, such as cockles on the recording medium resulting from the adhesion of ink droplets thereto.
2. Related Background Art
Traditionally, there has been a need for an ink jet recording apparatus to minimize the influence of wrinkles or a waving deformation (hereinafter referred to as cockling) formed on a recording medium when ink is discharged onto it in order to stabilize the recording performance, and maintain a constant gap between the surface of a recording medium and the recording head. Also, it is required to prevent a recording medium from floating from the platen toward the head in consideration of the fundamental properties thereof that cause it to curl easily if moisture or the like is present.
Conventionally, therefore, as examples to attain the objectives described above, there are apparatuses structured as given below. Firstly, as a recording apparatus disclosed in the specification of Japanese Patent Laid-Open Application No. 4-69264, there is a structure arranged to press a recording medium to the platen by means of a sheet pressure member on the upstream side in the feed direction of the recording medium. Secondly, there is known a structure as disclosed in the specification of Japanese Patent Laid-Open Application No. 61-95966 and Japanese Utility Model Laid-Open Application No. 3-29352, among others, in which a plurality of small-diameter holes are provided for a platen to effectuate the close contact of a recording medium with the platen by the application of suction force generated by use of means for generating negative pressure.
However, in accordance with the first prior art, in which the structure is arranged to press the platen by means of a sheet pressure member on the upstream side of the printing area, the anticipated effects are reduced more so as to give cockling or to allow a recording medium to float more easily if the printing width of a recording head is wider, and the distance is longer from the currently pressed position to the next position to be pressed, although this arrangement is still effective if the printing area is narrower, and also, the distance is shorter from the position where the pressure is given on the upstream side of the printing area in the sheet feeding direction to the next position where pressure is exerted (for example, the sheet exhausting roller pair). Particularly when recording images are formed in high density, a great amount of ink is impacted on the recording medium. As a result, a greater cockling occurs even to allow the recording medium to touch the printing head, thus leading to the formation of disturbed images or the clogging of the heading head.
In accordance with the second prior art, in which an arrangement is made to suck a recording medium by means for generating negative pressure, the apparatus is made inevitably larger, resulting in higher costs, as well as in louder noises made in sucking and exhausting air. Moreover, when recording media of different sizes are used, means for sealing the small-diameter holes should be arranged anew for those holes on the platen, which are not covered by any recording medium, and this sealing arrangement should be made in accordance with each different size of the recording media to be used, hence making it rather difficult to obtain the required suction force as desired.